The present invention relates to high power amplifiers, and in particular to gate modulation of high power amplifiers for efficient operation.
Telecommunications base stations use ultra linear radio frequency (RF) high power amplifiers for transmitting signals to remote communication devices such as cellular telephones. The amplifiers use transistors to amplify RF signals for transmission. The requirement of ultra high linearity dictates that the transistors be biased electrically in such a way that minimal distortion is imposed upon the amplified signal. Unfortunately, such biasing results in the transistor(s) requiring continuous electrical power, even when the magnitude of the signal to be amplified is zero.
Current high power amplifier designs for use in Code Division Multiple Access (CDMA) base stations have an efficiency of approximately 13% when operating at maximum rated output power. This low efficiency results in the need to disperse heat generated by the excess power consumed. It also results in base station packaging being physically large, complex and costly.
There is a need to reduce the power consumption of high power amplifiers without affecting the linearity of the amplification. There is a further need to reduce the need for large, complex and costly packaging for RF high power amplifiers caused by excess heat generation.
A high power RF amplifier utilizes dynamic biasing for transistors in an output stage of the amplifier. In one embodiment, as the magnitude of an RF signal to be amplified falls below a predetermined level, the biasing signal is turned off to reduce power consumption. A gate bias voltage is used to switch the transistors off and on. A low pass filter is employed to eliminate noise generated at the output of the amplifier caused by the instantaneous switching, while not impacting the amplifier""s response to low-high magnitude transients.
In a further embodiment, I and Q data from baseband digital data is sampled and buffered prior to being transformed and provided to a RF power amplifier. A gate bias signal is controlled based on current samples in order to control the power amplifier in a manner appropriate for the current samples when provided from the buffer. If the current sample and next samples are less than a threshold, the gate bias is removed. If the current sample and next samples are greater than the threshold, the gate bias is present.